Different effects of warming and cooling on the decomposition of soil organic matter in warm–temperate oak forests: a reciprocal translocation experiment

Abstract

A reciprocal soil monolith-transfer experiment was conducted along an altitude gradient to investigate the effect of climate change on soil carbon (C) processes in two warm–temperate oak forests in Baotianman Nature Reserve, Henan Province, China. Microclimate conditions, soil surface CO2 flux, and labile organic C were measured for in-situ and transferred soils at both high and low-elevation sites. The soil temperature at 5 cm depth was, on average, 3.27 °C warmer at the low-elevation site than at the high-elevation site. Net CO2 flux (911 g C m−2 13 months−1, 4.7 % of total C) of soil monoliths transferred from the high to the low-elevation site (simulating warming) was substantially (44 %) greater than for high-elevation soil monoliths incubated in situ (633 g C m−2 13 months−1, 3.3 % of total C) during 13 months of incubation. Increased extractable organic C (K2SO4-C) supply with warming partly explained the increase of soil CO2 flux. Simulated warming also significantly increased the temperature sensitivity (Q10 values) of soil organic matter decomposition. The positive linear relationship between microbial metabolic quotient (qCO2) and Q10 suggests a connection between microbial population and Q10 under warming conditions. Transfer of soil monoliths from the low to the high-elevation site (simulating cooling) substantially (30 %) reduced soil CO2 flux (383 g C m−2 13 months−1, 2.5 % of total C) compared with those incubated in situ (550 g C m−2 13 months−1, 3.5 % of total C). However, this was not accompanied by consistently opposite changes, to a similar extent, in labile organic C (microbial biomass carbon and K2SO4-C) and decomposition results (i.e., Q10 and R10, soil respiration at 10 °C), indicating that the soil organic matter decomposition process may not respond equally to cooling and warming. Different soil organic matter decomposition responses to cooling and warming should be considered for paleoecological modeling when both warming and cooling are involved in the changes in regional and global climates, particularly during the Holocene.